Can you link a C++ library from a C application?

I have cross compiled an open-source library (C++ based) using my G++ cross compiler. I am开发者_运维问答 now trying to use the outputted .a files in my C based application that is built using my GCC compiler... Is that possible?

Yes. Ensure that all functions you want to use are extern "C" and that you only use basic types on the functions you want to use.

If you use the same version GCC as you use G++ it should definitely not be any problem. Cross-version should be ok, but may have very minor incompatibilities. New GCC (3.0+) conform to the Itanium ABI so they'll be fine; they have a binary agreement on how to exchange & format data.

You will need to ensure that the C++ functions called from the C code are declared extern "C" and that their interfaces use only types that can be handled by C (simple types, opaque pointers, etc).

You will probably also need to link the application with the C++ compiler, rather than the C compiler, to ensure that the correct initializations are done for the C++ library. The C++ compiler used for the linking must be 'the same' as the one used to generate the library. That means either the same version of the C++ compiler or a compatible version of it. It usually means that you cannot link with CompilerA (from Vendor A) if the library was produced by CompilerB (from Vendor B); the C++ runtime conventions are such that different compilers (deliberately) use different schemes for supporting different features of C++.

You can link a C application to a c++ library, BUT you can only include header files containing valid C -- not C++ -- code, AND any c++ functions you call must have been declared with the extern "C" declaration.

The answer to your question is "yes" but as others have pointed out, there are some considerations, hazards & limitations to what you can do & how you do it.

Just recently in the course of covering this same topic with a client, I came across an article with a pretty good treatment of the topic. The article discusses things like calling C code from C++ code, calling C++ code from C code, linker considerations, function wrappers, exceptions, linkage specifications, and accessing C++ classes from C, etc.

Article: Mixing C and C++ Code in the Same Program

If the C++ library has C++ interfaces you cannot use them directly, you will have to create wrappers that are compiled as C++ but which have extern "C" linkage. The complexity of such wrappers will depend on the natuire of the interfaces, use of C++-only features such as classes, and function/operator overloading will require work to map an OO interface to a procedural one.

The easiest, least-hassle method to do this, assuming your C code is reasonably sane, is to simply build your C application with g++.

Remember, good C code almost always builds in a C++ compiler. Then there are no special considerations, no extern "C" statements to add, no ABI issues, etc, and you can easily use the C++ library to its fullest, regardless of how its functions are declared.